[kens]

What's stopping a government agency from "saving up" their hashing power so they could get majority control over Bitcoin if they needed to? Seriously, if you were the NSA, wouldn't this be a sensible thing to spend a few million dollars on? And they could use their mining hardware now, hidden through pools, so it would almost pay for itself. (Yes, I know I'm getting into tinfoil hat territory.)

[Frogolocalypse]

In practical terms a 51% attack is not good, but actually has a fairly straight-forward solution to solve. Change the PoW. A 51% attack can't steal your coins, only restrict your spending them for the length of time they are conducting the attack. So the issue isn't that you have 51% attack possibility, but that people think you do, and furthermore think you're going to abuse it. If a government attacked it, they'd simply hard-fork away from the mining algorithm, and millions of dollars of hardware investment gets flushed down the toilet.

[tepmoc]

200K antminter S9 will produce about 50% hashrate of current bitcoin network that cost about 300M$ not counting electricity (200MW). But that means they have to R&D themselves these chips if they want attack quick. Otherwise they won't getting that much hashpower in one piece.

If they decide slowly enter game, attack price will raise significantly since network difficulty will be adjusted as they will add more of their miners into network and their projected 50% hashrate will be just 25%

So realistically its about 1 billion $ to attack current bitcoin network.

[Klathmon]

Nothing I guess, but they also aren't saying ASIC based mining perfect, just that it's better than the alternative (GPU based mining algorithms)